Ruger 10/45 problem

After shooting a 10/45 I disassembled it for cleaning. When the pistol was reassembled the trigger would not set. I am now trying to disassemble the pistol again but the assembly on the back of the frame will not release where it can be removed. All I can do is move it about 1/4". It seams to be hung up on something inside the frame. I do not want to force it too much for fear of breaking something.